Jaw crushers are utilized in many applications for crushing hard material, such as pieces of rock, ore, etc. A jaw crusher has a movable jaw that cooperates with a stationary jaw. Between the jaws a crushing gap is formed. The size of the crushing gap is adjustable by means of a hydraulic cylinder which is connected to the movable jaw. Adjustment of the position of the movable jaw may be carried out to compensate for wear of wear parts and/or to adjust the size of the crushed material.
Occasionally un-crushable objects, sometimes called tramp material, enter the jaw crusher. Un-crushable objects expose the jaw crusher to large forces and will push the movable jaw away from the stationary jaw.
US 2003/0132328 discloses a crusher having a hydraulic cylinder holding the movable jaw in a desired position. When an un-crushable object enters the jaw crusher hydraulic oil is evacuated from the hydraulic cylinder to an accumulator.